Monday is the “drop dead” date for people whose computers are still infected with the DNSChanger Trojan to get rid of it. Those who haven’t may not lose Internet access entirely, but Paul Vixie, of the nonprofit Internet Systems Consortium (ISC), said, “some of them will lose the ability to look up domain names, which will stop their Internet access in most cases. Others will see significant slowdowns.”

It is not as if people — and enterprises — have not been warned, or had time to address the problem. The DCWG has offered assistance in detecting and getting rid of the malware for months. The DNSChanger Check-up page helps users tell if a system on their network is infected. Another page offers help in cleaning up that infection .

The malware, discovered in 2006, infected more than four million computers and routers. It wasn’t until November 2011 that the FBI and Estonian police, in what was called “Operation Ghost Click,” arrested six Estonians, charging them with multiple cybercrimes.

The FBI seized more than 100 command-and-control servers hosted in U.S. data centers. But if they had shut them down immediately, millions of victims would have been disconnected from the Internet right then. So, a federal judge approved a plan to have the ISC deploy and oversee substitute DNS servers.

Those substitute servers were originally supposed to be in place for 120 days, until March, but U.S District Judge Denis Cote ordered the deadline extended to give people more time to get rid of the malware.

Those servers will now come down Monday, unless the court grants yet another extension. And Internet Identity (IID) says that of last week there were still 300,000 or more systems infected. IID said 12 per cent of all Fortune 500 companies and 4 per cent of “major” U.S. federal agencies are still infected.

But security experts oppose another extension. Asked if the deadline should be extended again, Chester Wisniewski, senior security advisor with Sophos gave an emphatic “No.”

“The deadline should not have been extended the first time in my opinion,” Wisniewski said. “If the victims are infected by DNSChanger, they likely have other malware installed as well. If they can no longer get to the Internet, they will seek out assistance and get the help they need.”

Brian Krebs, author of the blog Krebs on Security, agrees. In a post last week , he noted, “DNSChanger may no longer be hijacking search results, but the malware still carries secondary threats and risks.” “It was frequently bundled with other nasty software, and consequently machines sickened with DNSChanger also probably host other malware infestations,” Krebs writes. “Additionally, DNSChanger disables antivirus protection on host machines, further exposing them to online threats.”

Vixie agreed. “It’s been long enough to help every user who is capable of being helped. At this point whoever is remaining will need to lose service to get fixed,” he said. But he added: “We could have used brownouts to get the point across more gently than the coming blackout. But this kind of ‘tough love’ is hard to get consensus on within an industry group like DCWG.”

Chester Wisniewski said he thinks the warnings to victims could have been more visible. “Rather than operate the DNS in perpetuity they should have immediately cut over to a warning page. If a site is taken down for copyright violations, you get a splash page from Immigration and Customs Enforcement or Department of Homeland Security, etc.,” he said. “Users should be directed to a warning page telling them that they are infected and direct them toward resources that can help clean them up.”

For those who have ignored their infection and lose Internet on Monday, Vixie said they should, “call their technical support path.”

The move is necessary, he said, because while the DNSChanger threat was essentially neutralized last November, “the victims are ‘the botnet.'”